1. Field Of The Invention
The present invention relates generally to apparatus for controlling deployment and retrieval of a tether, and more specifically to apparatus for moving tethered instruments to and fro in a conduit such as a sewer pipe.
2. Description Of The Related Art
The interior of a narrow conduit is inherently difficult to access, as when it comes time for its inspection or cleaning. For example, sewer pipes and like conduits routinely become obstructed by roots, dirt, grit, grease and encrustation which must be removed to keep the flow moving freely. Sewer pipe cleaning is often performed by guiding a spirally-ribbed, resilient ball through the pipe on a cable, the ball being driven from behind by water pressure.
The apparatus heretofore directed to this task is manually-operated and includes a cable spool supported on a frame comprised of a pair of A-shaped members. The cleaning ball is attached to the end of the cable and a crank handle is provided on the spool. In operation, the cable spool is positioned on its frame adjacent a manhole at the upstream end of a sewer pipe. Then, the ball and its trailing cable are fed into the pipe. A head of water is built up in the manhole behind the ball, driving it downstream. Cleaning is most effectively accomplished when the cable is played out so as to restrict the ball's velocity with respect to the water in the pipe because water rushing through the marginal space around the ball causes it to spin and scour the pipe's inner surface. In addition, water rushing past the ball at high velocity tends to wash solids ahead of the ball.
Fairly substantial obstructions can normally be cleared by "bouncing the ball", i.e. drawing it some distance upstream and then releasing it, driven by water pressure, against the obstruction. This entire process is known in common parlance in the trade as "balling out" a sewer pipe, or "sewer balling."
Despite its long and widespread use, the above-described manual sewer balling apparatus has several serious drawbacks. For example, since good cleaning requires the pressure of a considerable head of water behind the ball, pipes of any more than approximately eight inches in diameter are difficult to clean manually. The pressure required in larger pipes exceeds the strength and ability of the average operator to restrict the ball's velocity and to crank it upstream for bouncing against obstacles. Thus, the efficiency with which the manual apparatus can practically be used is limited to the strength of the operator turning the spool's crank handle.
Safety is also a problem with the manual apparatus. Unless removed, the crank handle spins freely in the bouncing operation, this having caused many injuries to operators attempting to control its motion. Bouncing also requires that the operator crank the heavy spool while in a bent position; this causes back injuries. In addition, bouncing often generates dangerous loops and slack in the cable. Finally, spools wound with sufficient cable to ball pipes of substantial length are heavy and, when mounted on a supporting frame, are cumbersome and difficult to position safely adjacent a manhole.
A powered apparatus has recently been used in this setting for the limited purpose of retrieving cable more quickly from conduits. That is, once a cable has been run through a conduit behind a ball, the ball is removed at the downstream end and this powered apparatus is engaged with the conventional manual spool and used to retrieve the cable alone. One such apparatus is fashioned from the power head of a chain saw wherein the saw's bar is replaced with a splined coupling. Unfortunately, this apparatus is unable to draw a ball upstream in a conduit against a head of water. And even when retrieving naked cable alone, it is heavy, noisy and dangerous. For example, snags in the cable are likely to pull the apparatus from the operator's grip.
Thus, there exists a need for a powered apparatus able to control a tether in a conduit during sewer balling and related operations. It should be capable of controlling a ball's downstream progress against a fairly wide range of pressure, including a substantial head of water. And, it should be able to draw a ball upstream against substantial pressure as well. Finally, it should be able to be positioned safely and securely adjacent a manhole, and should be simple to operate.